1. Field of the Invention
The present invention relates in general to a method for producing a thermoplastic nanocomposite comprising a polymer matrix having dispersed therein exfoliated silicate layers derived from a intercalated layered silicate. More particularly, this invention relates to such a process where the intercalated layered silicate is intercalated with a polymerizable lactam monomer, such that during the process the silicate layers are exfoliated due to polymerization of said monomer and dispersed in the polymer matrix to impart mechanical reinforcement.
2. Description of the Related Arts
Nanocomposites are a new class of materials which exhibit ultrafine phase dimensions, typically in the range 1-100 nm. Experimental work on these materials has generally shown that virtually all types and classes of nanocomposites lead to new and improved properties such as increased stiffness, strength, and heat resistance, and decreased moisture absorption, flammability, and permeability, when compared to their micro- and macrocomposite counterparts.
In regard to preparation of thermoplastic nanocomposites, it has been disclosed that swelling agents such as long-chain organic cations, and water-soluble oligomers or polymers can be intercalated or absorbed between adjacent layers of a layered silicate, such as smectite clay, to thereby increase the interlayer spacing between the adjacent silicate layers, so that polymer chains can be included between the silicate layers when mixing the layered silicate with a polymer melt. See for example, U.S. Pat. No. 5,552,469, WO 93/04117, Japanese Laid Open Patent Application Nos. 8-151,449, 7-207,134, 7-228,762, 7-331,092, 8-259,806, and 8-259,846. However, the layered silicate according to these methods for the most part can not be exfoliated into individual layers (but can only be swollen) to impart greater mechanical reinforcement to the polymer matrix. To the contrary, the swelling agents sometimes precipitate out and decrease the mechanical properties of the composites.